This invention relates generally to communications framing circuitry and, more particularly, to a system and method for selecting the frame synchronization structure in a communications link.
Generally, communication protocols form the information to be sent into a frame of data words. A known overhead word is embedded in the information string at the point of transmission. At the point of reception the known overhead word is used to synchronize the information into a frame structure so that the data words can be recovered. For improved reliability the known overhead words remain constant. That is, the sync structures are preset, independent of the data.
However, there are circumstances where the use of the convention known overhead word is inconvenient. For example, in high bit error environments it may be useful to reduce the length of the overhead once the received information stream is synchronized to reduce the probability of losing sync. Likewise, it may be useful to increase the length of the overhead word in high bit error environments when a received information stream is not yet synched to improve the likelihood that synchronization will occur on a valid overhead word.
There are also occasions when the data forms in words are similar enough to the sync words, similar enough to cause synchronization errors. There is no flexibility in protocol synchronization structures that permits the sync words to be modified in special circumstances.
Even if communication links were enabled with different types of overhead words for different circumstances, no circuitry is available to easily change the selection and use of overhead words on either the receive or transmit end of the communication link.
It would be advantageous if the synchronization structure in a communication protocol could be modified in response to the BER environment.
It would be advantageous if the synchronization structure could be modified in response to the type and form of the data words being communicated.
It would be advantageous if only selected parts of a known sync word could be used in circumstances when it is not desirable to use the entire sync word.
It would be advantageous if overhead word used to synchronize frames in digital communications could be made selectable. It would be useful if the content of the word, the number of bits in the word, and the arrangement of bits in the header section were selectable by the user.